Reaction rates and mechanisms in the oxidation of organic sulfur compounds by perbenzoic acid generated in situ from benzaldehyde autoxidation were investigated. Dibenzothiophene and diphenyl sulfide were utilized as model sulfur compounds typical of those present in residual oil and coal. The aromatic nature of a fuel medium was simulated by bromobenzene solvent. Reaction samples were quantitatively analyzed primarily by means of high-pressure liquid chromatography. Diffusion of oxygen, peracid decomposition, and direct oxidation of aldehyde by peracid were found to limit the formation of peracid. Activation energies for decomposition of the peracid and for direct oxidation of the aldehyde by peracid were obtained and used to explain the maximum in oxidation efficiency with respect to temperature observed for dibenzothiophene. Perbenzoic acid was found to be selective in oxidizing diphenyl sulfide and dibenzothiophene to the corresponding sulfoxides and sulfones. At 75°C, diphenyl sulfide was only oxidized approximately twice as rapidly as dibenzothiophene, in contrast with the higher rates reported by other investigators. Both sulfur compounds were found to inhibit the rate of benzaldehyde autoxidation.
